The present invention relates to an air-fuel mixture generating device equipped with a diaphragm-type fuel pump, a fuel injection valve and a manual fuel pump, and in particular, to an air-fuel mixture generating device which is adapted to be employed, as an alternative to the conventional ordinary carburetor, for the intake system of an air-cooled two-stroke gasoline engine of the crankcase precompression type, which is particularly suitable for powering portable working machines and the like.
For the intake system of a small air-cooled two-stroke gasoline engine of the crankcase precompression type (hereinafter referred to simply as an internal combustion engine), such as those used to power portable working machines such as chain saws or bush cutters, there is frequently employed, as an air-fuel mixture generating device, a floatless diaphragm-type carburetor equipped with a diaphragm-type fuel pump which is designed to induct fuel and to inject pressurized fuel in conformity with pressure changes (pulsating pressure) inside the crankcase of the internal combustion engine in order to ensure a stable supply of fuel to the engine irrespective of the posture of the engine.
However, it is difficult, with such a diaphragm-type carburetor, to precisely control the quantity of fuel in relation to the intake air (control of air/fuel ratio) and to achieve sufficient atomization of fuel and accurate response to the pulsating pressure, thereby making it difficult to effectively take measures for purifying the exhaust gas.
Under the circumstances, there has been recently proposed, as an alternative to the aforementioned carburetor, an air-fuel mixture generating device which is equipped with a fuel injection valve in addition to the aforementioned diaphragm-type fuel pump.
In an air-fuel mixture generating device of the aforementioned type, a diaphragm is disposed inside a main body that has a construction similar to that of a carburetor, a pulsating pressure chamber to which the pressure of the crankcase is transmitted is provided on one side of the diaphragm, and a pump chamber for inducting fuel and injecting it to a fuel passageway is provided on the other side of the diaphragm. The diaphragm is actuated (reciprocating movement) by taking advantage of the pressure changes (pulsating pressure) in the crankcase resulting from the movement of the piston of the internal combustion engine, i.e., the decrease in the pressure as the piston is moved upward and the increase in the pressure as the piston is moved downward, thereby enabling a pressurized fuel to be fed from the pump chamber to the fuel passageway and also enabling the fuel inside the fuel passageway to be pressurized. At the same time, the aforementioned fuel injection valve is allowed to open with a predetermined timing (for example, at the moment of the initiation of the suction stroke) for a predetermined period of time (for example, 1 to 3 milliseconds), depending on the operating condition of the internal combustion engine, to thereby enable the pressurized fuel in the fuel passageway to be injected into the intake system (for example, an intake passage portion located on the downstream side of the throttle valve) so as to be mixed into the inducted air, thereby producing an air-fuel mixture.
However, since the diaphragm-type fuel pump according to the aforementioned air-fuel mixture generating device is designed to be actuated by taking advantage of the pressure changes (pulsating pressure) inside the crankcase, the quantity of fuel to be injected by the diaphragm-type fuel pump is caused to greatly increase as the internal combustion engine is operated at a high speed (for example, 6000 rev/min or more), resulting in an excessive increase in pressure of the fuel disposed inside the fuel passageway (for example, the pressure will be increased up to nearly 0.1 MPa). As a result, the fuel is caused to be injected excessively from the fuel injection valve, thereby raising the problem that an excessively rich air-fuel mixture is fed to the combustion-actuating chamber of the internal combustion engine.
It may be considered, as one of the countermeasures for solving this problem, to incorporate a pressure-adjusting means such as a fuel pressure regulator, etc., into the pump chamber or the fuel passageway. However, the incorporation of the pressure-adjusting means such as the aforementioned regulator will make the resultant structure very complicated, thus increasing the manufacturing cost thereof.
The present invention has been made with a view to solving the aforementioned problems. It is, accordingly, an object of the present invention to provide an air-fuel mixture generating device which is equipped with a diaphragm-type fuel pump and a fuel injection valve, and is capable of preventing an excessive amount of fuel from being injected from the fuel injection valve, even if the internal combustion engine is operated at a high speed, without making the air-fuel mixture generating device complicated in construction and without greatly increasing the manufacturing cost thereof.
With a view to attaining the aforementioned objects, the present invention provides an air-fuel mixture generating device which essentially comprises:
a main body equipped with a diaphragm-type fuel pump which is designed to induct fuel and to inject the fuel into a fuel passageway in conformity with pressure changes inside the crankcase of the internal combustion engine;
a fuel injection valve attached to the main body for injecting the fuel of the fuel passageway into an intake system of the internal combustion engine with a predetermined timing;
a manual fuel pump attached to the main body for filling the fuel passageway with fuel on an occasion when the diaphragm-type fuel pump is not actuated, the manual fuel pump having an inlet port which is communicated with the fuel passageway; and
a pressure-adjusting valve disposed at the inlet port of the manual fuel pump, thereby enabling it to act not only as an intake valve on an occasion when the manual fuel pump is actuated but also as a relief valve for allowing the fuel inside the fuel passageway to escape into a manual pump chamber of the manual fuel pump on an occasion when the pressure of fuel inside the fuel passageway exceeds a predetermined pressure.
In a preferred embodiment of the air-fuel mixture generating device according to the present invention, the diaphragm-type fuel pump is constituted by a diaphragm disposed inside the main body, a pulsating pressure chamber formed on one side of the diaphragm for receiving a pulsating pressure of the crankcase, and a pulsating pressure pumping chamber formed on the other side of the diaphragm for inducting fuel and injecting the fuel to the fuel passageway.
In another preferred embodiment of the air-fuel mixture generating device, it further comprises an intake valve which is formed at a portion of the diaphragm located between the pulsating pressure pump chamber and a fuel intake passageway portion, and an injection valve which is formed at a portion of the diaphragm located between the pulsating pressure pump chamber and the fuel passageway.
In another preferred embodiment of the air-fuel mixture generating device, an escape valve is disposed at an escape port of the manual fuel pump, the escape valve being designed to be closed when the pressure inside the manual pump chamber is less than a predetermined pressure, and also designed to be opened when the pressure inside the manual pump chamber is increased higher than said predetermined pressure.
The internal combustion engine to which the air-fuel mixture generating device of the present invention can be preferably applied is an air-cooled two-stroke gasoline engine of crankcase precompression type, wherein the injection port of the fuel injection valve is disposed on the downstream side of the throttle valve of the intake passageway.
With an air-fuel mixture generating device of the present invention constructed as described above, since fuel is required to be manually introduced into the fuel passageway at the time when the diaphragm-type fuel pump is not actuated, i.e., before the internal combustion engine is started, the air-fuel mixture generating device is equipped with the aforementioned manual fuel pump. When the manual fuel pump is actuated before starting the internal combustion engine, the fuel in a fuel tank is conducted, preferably, through the fuel intake passageway portion and the pulsating pressure pump chamber to the fuel passageway by the pumping action effected by the opening and closing movements, acting in opposite phase, of the pressure-adjusting valve disposed at the intake port of the manual fuel pump and of the escape valve disposed at the escape port of the manual fuel pump. When the internal combustion engine is started under this condition by means of a recoil starter, for example, the fuel injection port is caused to open with a predetermined timing (for example, at the moment of initiating the suction stroke), thereby enabling the fuel inside the fuel passageway to be sucked and fed to the intake system (for example, an intake passage portion located on the downstream side of the throttle valve) so as to be mixed into the inducted air at a proper ratio, the resultant air-fuel mixture being fed to the crankcase and combustion actuating chamber of the internal combustion engine so as to be ignited and explosively combusted by means of an ignition plug, thus realizing a self-sustaining normal rotational operation of the engine.
In the normal operation of the engine after the start-up, the pressure changes (pulsating pressure) inside the crankcase, i.e. a decrease in pressure in the ascending stroke of piston and an increase in pressure in descending stroke of piston, are transmitted to the pulsating pressure chamber of the diaphragm-type fuel pump, thereby driving the diaphragm (reciprocating movement). Due to the pumping action resulting from the vertical motion of the diaphragm, the fuel is sucked into the pumping chamber from the fuel tank, and then, fed from the pulsating pressure pump chamber to the fuel passageway so as to be compressed therein. During the normal operation of the engine, the fuel injection valve is caused to open with a predetermined timing (for example, at the moment of initiating the suction stroke) for a predetermined period of time (for example, 1 to 3 milliseconds), depending on the operation condition (such as the quantity of inducted air) of the internal combustion engine to thereby enable the pressurized fuel in the fuel passageway to be injected into the intake system (for example, an intake passage portion located on the downstream side of the throttle valve) so as to be mixed into the inducted air.
When the internal combustion engine operates at a high rotational speed, the pressure of fuel in the fuel passageway becomes higher due to the pumping action of the diaphragm. However, when the pressure of fuel in the fuel passageway becomes higher than a predetermined magnitude (for example, 0.05 MPa), the pressure-adjusting valve which is disposed at the intake port of the manual fuel pump is forced to open, thereby allowing the fuel inside the fuel passageway to escape into the manual pump chamber of the manual fuel pump. Subsequently, when the pressure inside the manual pump chamber becomes higher than a predetermined value, the escape valve which is disposed at the escape port of the manual fuel pump is forced to open, thereby allowing the fuel inside the manual pump chamber to return to an externally disposed fuel tank.
It is possible in this manner to inhibit the pressure (maximum pressure) of fuel inside the fuel passageway from exceeding the aforementioned predetermined value. As a result, it is possible to prevent injection of an excessive amount of fuel from the fuel injection valve and thereby the supply of an excessively rich air-fuel mixture to the combustion actuating chamber of the internal combustion engine.
According to the air-fuel mixture generating device of the present invention, a check valve which is indispensable for the manual fuel pump to be essentially employed in a case where the feeding of fuel is performed by making use of a diaphragm-type fuel pump together with a fuel injection valve is utilized in such a way that when the pressure of fuel inside the fuel passageway is less than a predetermined value, i.e., when the manual fuel pump is not operated or when the internal combustion engine is not in a state of high rotational speed, the check valve functions as a check valve as inherently intended, but when the pressure of fuel inside the fuel passageway exceeds the predetermined value, the check valve functions as a pressure-adjusting valve, i.e., a relief valve, for allowing the fuel inside the fuel passageway to escape into the manual pump chamber. Therefore, it is not necessary to integrate any additional fuel pressure regulator into the air-fuel mixture generating device. Thus, what is required in the device of the present invention is to suitably adjust the pressure of a spring, such as a coil spring employed in the check valve, thereby making it possible to prevent the device from becoming complicated in construction and to derive savings in the manufacturing costs thereof.
Additionally, with an air-fuel mixture generating device of the present invention, since the quantity of fuel can be controlled by means of the fuel injection valve, it is now possible to control the feeding quantity of fuel in relation to the quantity of inducted air (air/fuel ratio) with higher precision as compared with the conventional diaphragm-type carburetor, and to improve the atomization of fuel and the accurate response to the pulsating pressure, thereby making it possible to effectively purify the exhaust gas. Moreover, since the air-fuel mixture generating device of the present invention is constructed in almost the same manner as the conventional ordinary diaphragm-type carburetor except that the fuel feeding portion is modified with the fuel injection valve, the air-fuel mixture generating device of the present invention can be easily incorporated, in place of the conventional carburetor, into the conventional internal combustion engine.